Once you reach Chapter 6 there is an area available called the "Waterless Bridge" on level 8.
You will find a merchant there that sells the two materials to craft "Compact Scobe ß". They are "Glass Shard" (150 rubies) and "Scrap Iron" (200 rubies). Buy as many of these materials as you please.
Now go back to the Tinkerer in Ebel City and craft as many "Compact Scobe ß" as possible for 3000 rubies each. Now turn around and sell it to the shop owner for 4100 each.
Each one you sell will net you 750 rubies in profit. It doesn't seem like much, but after you build up your funds to do a lot at one time, it really starts to add up.
Once you find yourself with 500,000 rubies just start buying everything you can out of the Clothing Store.